DIMENSIONS OF SUSTAINABILITY

Abstract

No agreed definition of sustainability has emerged. As a
result, people define sustainability in the ways that suit
their particular applications, often times with no explicit
evidence and recognition of the exact meaning being implied.
We analyze several definitions, and find that while there is
no common meaning, the definitions can be organized according
to a common set of dimensions. Space and time are common in
systems analysis and characterize all the definitions
considered. Added to these are structural and perceptual
dimensions. Our analysis indicates that sustainability should
be treated within the framework of a total system, taking into
account the ecological, social and economic as components of
the system. It is impossible to sustain one part of the total
system without the others being involved. It is therefore
more reasonable to speak about systems sustainability instead
of sustainability of resources or sustainable development
(economic bias with ecological concerns), or sustainability of
ecosystems (ecological bias with economic concerns) . We try
to merge ecology and economy into one system coming up with
the conditions for sustainability instead of defining the term
in an exact way.

Key words

A Systems Perspective on Sustainability

What do people mean when speaking about sustainability?
Sustainable yield management emerged as the dominant paradigm
in the early twentieth century. The promise of sustainable
yield was continuous supplies of fish, food, and fiber,
without degrading natural resources. The practice of
sustainable yield management has been a series of crises. The
Brundtland Commission report, Our Common Future (WCED, 1987),
re-energized interest in sustainability, however since that
time, no common definition of the term has come forth, despite
considerable literature appearing in both the scientific and
public press. See for example, the special issue of
Ecological Applications - Vol.3, No.4, Nov. 1993 - for an
extensive discussion on various sustainability problems.

Most sustainability definitions originate from the
relationship between humans and the resources they use. For
example, among the 75 definitions of sustainability collected
from students at Oregon State University 65% explicitly
identified sustainability as resource management and use
practices. Wimberly (1993:1) states that "to be sustainable
is to provide for food, fiber, and other natural and social
resources needed for the survival of a group -- such as a
national or international society, an economic sector, or
residential category -- and to provide in a manner that
maintains the essential resources for present and future
generations". Gale and Cordray (1991) look at eight and later
(1994) at nine types of resource sustainability.

Some of the definitions are very descriptive and focus on
humanitarian and ethical aspects. According to Solow (1991),
"sustainability as a moral obligation is a general obligation,
not a specific one." Norton (1992:25) argues that
"sustainability is a relationship between dynamic human
economic systems and larger, dynamic, but normally slower
changing ecological systems, such that human life can continue
indefinitely, human individuals can flourish, and human
cultures can develop - but also a relationship in which the
effects of human activities remain within bounds so as not to
destroy the health and integrity of self-organizing systems
that provide the environmental context for these activities".
However in that same book we find the definition reversed when
an ecological system is termed healthy "... if it is stable
and sustainable" (Haskell, et al., 1992:9). In another
definition Costanza (1992:240) leans on the systems
properties, stressing that "sustainability... implies the
system's ability to maintain its structure (organization) and
function (vigor) over time in the face of external stress
(resilience)".

Part of what makes defining sustainability controversial is
that the issue actually brings ecological problems from the
realm of pure science to the everyday life of people.
Defining sustainability connects abstract environmental issues
with people's personal and commercial interests. As a result,
sustainability becomes one of those terms which is easier to
understand, than to explain.

In many cases the sustainability goal is being applied only to
the economic part of the development process and the
ecological part is only considered as a background on the
stage where economy is developing. Nearly all sustainable
resource issues come from this economic prerogative, with the
attempts to make the ecological resources last as long as
possible in support of economic development. Many issues of
sustainable agriculture also belong to this economic domain.
There is a relatively smaller portion of sustainability
concerns that prioritize the ecological part of the problem
(Nash, 1991). We mostly find them in the green movement
(Greenpeace or Earth First, as the extreme presentation of
these concepts), or in theories of "deep ecology" (Devall and
Sessions, 1985). In this approach the goal of sustainability
is primarily imposed on natural systems, which are to "remain
in pristine conditions" (Taylor, 1986).

Generally, in most of the literature, the ecological part and
the economic part are considered as separate systems operating
independently. Effort is made to compare the two systems
(Holling et al., 1993) or to look at their coevolution, trying
to combine their dynamics. Ecology is being incorporated into
economy, giving rise to the new science of ecological
economics (Costanza, 1991).

Still there is relatively little effort to look at the
economic and ecological parts within the framework of one and
the same system. In terms of sustainability this becomes
especially crucial, because it is not possible to speak about
long-term development of one of the subsystems without taking
into account the other. It seems to be much more reasonable
to think general system sustainability, realizing that the
economic and ecological components are to be considered
together in their interplay.

Within the systems approach it becomes clear that there are
numerous feedback links between the social, biological and
physical parts and that it is not possible to sustain one part
without some trade-offs from the others. In their
"sustainable" development over the last 12 000 years humans
have usually neglected the sustainability of nature, trying to
build the world in their own way, reconstructing the nature,
trying to mold it to suit their needs best. The few
cautioning voices were hardly heard and only after humans
became a geological power (Vernadsky, 1978) did they realize
that they were about to pass the point of no return, that the
technocratic approach, too, has its drawbacks, and that it
may not suit the aesthetics and morals of all and may not
itself be sustainable. However there is great inertia in
human societies. Some count on new technologies that should
solve all environmental problems, others do not care, still
others care and understand that something has to be done but
are not ready to change their habits and life styles. The
development continues and the environments change. The
overall problem is that the emerging environments may be quite
different from what we are used to, what we expect for human
habitat, and change may be irreversible.

Do these created technocratic environments suit the needs of
the majority? Can they be sustainable? With no clear answers
to these questions there is the other group of definitions of
sustainability, that tend to prioritize the changes within the
human as part of the biosphere, the trade-offs and sacrifices
that people may be willing to bring in order to keep some of
the natural control mechanisms and natural cycles, instead of
totally depending on the artificially imposed human
management.

For this purpose it is necessary to merge all the subsystems
that make up the human life support system, to look at them in
their interplay and to decide how to make the whole system
sustainable. Starting with a brief exploration of the
resource sustainability types, we will look at the other
definitions of sustainability, primarily focusing on the
concept of system sustainability.

Spatial Dimensions of Sustainability

Gale and Cordray (1994) in their sociological study of various
attitudes toward sustainability have come up with the
following types:

Ecosystem Insurance (EIN) - is to insure ecosystem diversity
against ecological disaster by applying two types of
management: some ecosystems are to supply resources, others
are protected in natural conditions.

Putting aside the possible critiques of this typology and its
appropriateness, let us use it as an example of the variety of
existing approaches to sustainability and see what are the
inherent scales for the different approaches. Let us only
note that actually the listed sustainability types do not
present the different possible designs of sustainable systems,
but rather deal with the rationale that is used to promote
sustainability. This typological study immediately refers us
to the varying understanding of sustainability, that
corresponds to the different ideas and priorities set up by
the proponents.

In systems analysis there are usually three dimensions along
which a system can be considered. These are time, space, and
structure. It is within these dimensions that we choose the
level of accuracy and the scales in which the system is
analyzed. The spatial dimension represents how the system is
represented in space, what spatial components are identified,
what are the spatial borders of the system and what are the
links to other systems across the borders. The temporal
dimension describes the level of resolution for system
dynamics in time, the time step of analysis, the temporal
events that should be either singled out or lumped together.
And finally the structural dimension is the level of detail
that is chosen to describe the processes and functions in the
system, the variables and the links between them.

The different definitions of sustainability assume different
scales and resolutions within the three dimensions. At a
first glance the temporal scale is less informative because
practically all sustainability definitions tend to depict
sustainability as extending to infinity - what else would we
be anticipating by this notion. The spatial dimension brings
more insight. In Figure 1 we tried to arrange the nine
sustainability types along the spatial axes. The available
nine points are clearly not a sufficient sample for
statistical analysis, however it is interesting to note that
the economically dominant sustainability issues tend to the
smaller, local scales: both the designed systems and the
interested groups are smaller, more localized. On the
contrary, there are hardly any applications that would strive
for globally sustainable economic systems. Surprisingly in
the global level most of the concerns are usually about the
biosphere as a system with the ecological focuses and
priorities rather than the economic ones. This observation
leads us to the more general question about the possible
spatial scales on which sustainable systems are to be
designed.
Looking at how ecosystems and economies operate, we may note
the importance of feedback mechanisms that control and adjust
the processes in systems. One of the reasons why market based
economies proved to be most efficient is because they employed
a number of self-regulating mechanisms either operating at the
local scale or networking together the locally operating
subsystems into a higher level system with efficient
feedbacks. Cooperation, but mostly competition and prices
based on demand and supply constantly tuned the overall system
functioning. At the same time the presumably more rational
and efficient systems of planned economy failed to really
account for all the cause-effect links and factors and result
in constant malfunctioning of the economic mechanism. The
feedbacks inherent to systems work independently of human
errors and will.

However the ecological and economic components of systems
operate in significantly different scales. The ecological
feedbacks are generally long both in time and space. The
feedbacks and in socioeconomic systems are rather short
(Miller, 1992: 139). The problem with sustainability is how
to make the ecological feedbacks shorter to incorporate them
into the economic and social subsystems, how to mirror the
regional and global environmental outcomes of our everyday
life in something we can feel and evaluate locally, right on
the spot, at home? An economic crisis, for instance, almost
immediately affects our everyday life - prices change, income
drops, etc. To close the loops of system sustainability we
need to map the global environmental change in something we
use and care for locally. Of course an overall price tag
associated with all our activities could do the job, but
unfortunately we still do not price ecological commodities in
an appropriate and unambiguous way.

For general sustainable systems we need to hypothesize a
spatial level at which feedback links impose self-control on
the subcomponents of the system. There need to be mechanisms
that directly feedback the ecological consequences of human
behavior into everyday life. The environmental degradation is
usually either remote in space, happening in distant
localities, in other countries or continents, or relatively
slow, delayed for further generations to cope with. The
institutional mechanisms that are supposed to feedback such
ecological responses are usually either not in place or not
yet efficient enough. Until larger scale feedback mechanisms
are created for the overall functioning of sustainable
systems, we should try to operate at the lowest level creating
small scale sustainability in the individual or family level.
This calls for special efforts in educational and awareness
building programs that influence and form the value sets and
human behavioral patterns.

Values in Sustainability

We therefore see that another dimension lies in the way the
domain of human values is structured. The first possible
values dichotomy in the approaches towards sustainability is
between the economic and ecological focuses, between
anthropocentric and ecocentric attitudes. On the one hand we
have anthropocentric definitions that assume maintenance of
the human well-being in the traditional consumers society
(DPS, DSS, HBS, GPS in Gale and Cordray's typology). In all
these cases it is assumed that humans are the most important
part of the ecosystem and ecosystem function is sustained
primarily for their benefit. On the other hand we can identify
the ecocentric approaches to sustainability, where the
ecological well-being of the whole planet or of a certain
region is emphasized regardless of the direct benefits of the
human population inhabiting it (GNP, EIS, SSS, EIN or EBS).

Going further on in classification (Fig.2), we find that among
the ecocentric definitions there are two structurally distinct
approaches: one which may be called "true ecocentric", which
is based on faith that in fact the human species is no better
than the others and that the humanity should lower its
ambitions and needs. The other ecocentric approach is
actually an anthropocentric one, since it stresses the
ecological priorities because it understands that the only
strategy of sustainable survival for the human being is to
limit itself to the ecologically feasible level. In the first
case we make our decisions in favor of ecological benefits as
a result of our faith and belief in nature and species rights,
while in the second case we basically act because of our
wisdom and understanding that in the long run the humans will
only benefit from nature conservation and harmony, and
actually choose the priority of ecological interests based on
logic and some knowledge.

In turn the anthropocentric approaches may be focusing either
on economic or on social values and benefits. Accordingly,
the decisions are being made to maximize either the social or
economic criteria. It might be argued that eventually the
ecocentric and anthropocentric approaches tend to get closer
merging together as we consider the long-term evolution at the
global scale of the human population. In this case some of
the aspects of global ecology become important from the
viewpoint of human health and aesthetic benefits. However it
should be also realized that for this factor to become
meaningful we must assume a total revolution in human
perception of its role and place in modern world as well as
its existing living standards and priorities. It is not likely
that general public is ready to take up these other standards
immediately.

Referring back to figure 1, we add another dimension to the
picture. Let us look at the system sructure, considered at
increasing levels of resolution or desegregation. We may
argue that there is a correspondence between the resolution or
the amount of information used to describe the structure of a
system and the attribute of human values, prevailing in the
system. The aggregated simplistic approach with few feedbacks
taken into consideration, with little understanding of the
processes, and little concern about the longer term and larger
scale effects in the system will probably generate a
simplified anthropocentric approach with the prevailing
economic set of values. The limited amount of information
about the links within the system and with the rest of the
world does not stimulate awareness about the possible remote
outcomes of human activities, the ecological components are
treated only as resources that are in place to support the
human component and the major concern is the optimization of
resource uptake and processing. As more details are taken
into account, more information about the feedbacks is
considered and the system is analyzed as a whole with more
links and processes, we gradually shift to the more
ecologically oriented value sets and eventually arrive at the
ecocentric value set placed at the other end of the
structure/value axis. As a result we may look at types of
sustainability in a 3 dimensional space with the two domains
in Fig.3 representing the two extreme cases: on the one hand
(A) sustainability can be viewed as of a purely economic goal
to serve our local momentary needs; in the other case (B) we
are mostly concerned with preserving the whole biosphere for
its own sake and for as long as possible. In one case we
operate in terms of a simplified model, looking only at the
sustainability of resources provided by the nature. In the
other we draw a holistic picture in which humanity acts within
the biosphere as its element.

Other definitions of sustainability fit somewhere in between.
However we still must admit that it is mostly the rationale,
the human logic of sustainability that differ and that we
class, rather than the sustainable system design.
Adding the temporal scale in this diagram we want to show
that, while all sustainability definitions emphasize
maintaining a particular system to infinity, still we note
that the anthropocentric approaches tend to operate on lower
scales, being concerned with relatively short term systems
(local economies, communities, etc.).

Dynamics of Sustainability

The temporal scale for evaluating system sustainability also
gives additional insight. The temporal dimension shows the
dynamics of sustainable systems, how and why they change in
time. It may be interesting to compare the sustainability
notion with that of stability.

Instead of "sustainability" in ecology, the topic usually was
"stability". Ecological stability has been discussed in
extensive literature. Both general biological and rigorous
mathematical definitions have been suggested. Sustainability
is still lacking both.

According to the classic definition of stability we assume
that there is a certain state or trajectory that the stable
system returns to after being disturbed within certain limits
(Fig.4). The property of stability was mostly analyzed within
the framework of ecological systems, described in terms of
such variables as population number, biomass, density,
concentration. Most often the system was considered as
operating on its own and stability was sought as its intrinsic
feature. In this case the dynamics of the system were
considered as self-contained with the goal of the system
imbedded into it. Human social and economic activities were
considered as external, causing perturbations and the major
issue was whether the system was stable enough to accept and
damp out these perturbations, maintaining its ecological
natural origin.

The notion of sustainability comes into play when we realize
that we cannot delimit the system in such a way that all the
essential links, inputs and outputs can be taken into account.
Pristine ecosystems, which can be separated from the human
world, are hard to find (Botkin, 1990), so the natural
ecological system operates in a world of human social
relations, which are much more difficult to bound, predict and
understand. Actually it is still just the other way round,
but for particular ecosystems the effect of humans already
turns out to be crucial and as humanity continuous its
expansion its environmental impact becomes dominant. Most
important is that the social values and as a result the goal
functions, the indicators that an individual or system tries
to optimize as it develops, are under constant change, because
of constantly changing perceptions and priorities within the
societies. Therefore in case of analyzing sustainability the
goal may be imposed on the system externally. The sought
state or trajectory of the system is to be changed and the
question is whether the system has internal resources to
respond appropriately or if there exist additional external
controls that can bring the system to the newly set dynamics
(Fig.5).

Robinson (1991) stresses that sustainability calls for
maintenance of the dynamic capacity to respond adaptively.
Instead of analyzing the system structure in order to
understand its behavior and the state or dynamics that it will
demonstrate, we are now investigating the flexibility of the
system to change according to the changing goals and controls.
With the system displaying the behavior presented by
trajectory A, suppose that due to some changes in the values
and social perceptions, we now want the system to follow
trajectory B. If we can find the appropriate control
mechanisms and change the system parameters or structure in
such a way that the system will follow trajectory B, then we
may call our system sustainable. It should be noted that in
this case human decision makers, take the very responsibility
of constantly managing the system in such a way that this,
maybe unnatural, equilibrium is preserved. Sustainability
appears as dynamically maintained stability.

In one of the definitions quoted above, an ecological system
is called healthy "if it is stable and sustainable" (Haskell
et al., 1992:9). We would argue that sustainability is a
broader notion, which encompasses stability and should refer
to the whole system level rather than only to the ecosystem
one.

The stable state is being achieved due to some natural
intrinsic mechanisms. System sustainability assumes constant
management. The system will be sustainable if there exists
such a management scenario, that will bring it to the desired
state or dynamics. It will be unsustainable if the management
scenario does not exist, or if it cannot be applied due to
some external conditions (say, financial limitations). In
turning to the sustainable development paradigm society in a
way takes a greater responsibility. Sustainability is always
defined within the particular domain in the values set. That
is, the property of sustainability is dependent upon the human
requirements imposed on the system.

If we could create a socioecological model that would take
into account not only the ecosystem biological and physical
processes, but would also describe the social and economic
relations as functions of the other system components, then
probably we could go back to analyzing system stability. In
the sustainability analysis we admit that there is so far no
understanding of how and why decisions are made, what actually
drives human priorities and values. We are not yet ready to
incorporate these factors in a formalized fashion for further
analysis within one single model. Therefore we are analyzing
system controllability instead of stability to provide for the
changing social values and priorities. Or as Salwasser
(1993:587) puts it: "sustainable development is a moving
target. It has multiple dimensions, scientific, economic, and
political, many of which are not amenable to scientific
illumination".

This brings us back to the notion of a common socioecological
system for analysis. In order to achieve the sustainable
dynamics we have to match the desirable behavior produced by
the social values system with what is possible on the
ecological part. There are always certain limits to the
adaptability of the ecological component and it should not be
overstrained. In a certain way this can be considered as a
dynamic stability, which is being achieved by both managing
the ecological subsystem and molding the social goals in an
adaptive way.

The social component that produces the goals is also a
function of the environment in many cases to a much greater
extend than we even realize. In our approach to
sustainability analysis we adopt the idea of a close link
between the social systems and their carrying environments, as
it has been suggested by Gumilev (1989) in application to the
development of ethnoses in conjuncture with their carrying
landscapes. We observe worldwide that there is a correlation
between the state of the environment and the socioeconomic
status of the region. The higher economically developed
nations usually have higher environmental standards and
concerns. However, we may also observe sustainable
environments in the pristine areas with very low living
standards and primitive economies. The most important
prerequisite of sustainability is the balance between the
social desires and ecological capacities. This brings us
finally to the following attempt to describe sustainability in
terms of a set of value conditions.

Conditions for Sustainability

Attempts to find an exhaustive definition for sustainability
seem to be quite futile - there are too many nuances sprouting
from the particular applications and implementations of the
term. In such a situation it might be more productive if
instead of giving precise definitions, we follow the axiomatic
approach and focus on describing the conditions that the
system is to comply with to achieve sustainability. The
axiomatic approach is widely used in abstract sciences such as
mathematics or logic and result in many productive
applications, even though at first sight it may seem that this
leads to cyclic definitions. Deciding about the necessary
conditions for sustainability instead of defining it, may
serve as a basis for building consensus between various
interested parties, in a way making clear the common ideas
that sustainability necessary implies.

Such necessary conditions may be formulated as follows:

1. the system does not cause harm to other systems, both in
space and time;
2. the system maintains living standards at a level that does
not cause physical discomfort or social discontent to the
human component;
3. within the system life-support ecological components are
maintained at levels of current conditions, or better.

We may also call this a perceptual definition because it is
based on a series of terms which we do not know how and do not
intend to define. At the same time their meaning is usually
intuitively implied, when considered in some particular
instances. We do not specify what is "harm" or "better", or
what does "discomfort" or "discontent" mean, however in each
application we may assume a procedure to measure these
indicators.

The first condition is quite obvious if we want to look at a
system in the higher scale as part of another system. If the
"bad things" are exported outside the system, the
sustainability of the system can not be considered, because
then we automatically have to assume that something else "bad"
can be imported from outside. This is related to an important
assumption we have to make when delimiting the system. We
want the parties involved to admit that everything they do may
be also done by the other interacting parties locally and/or
globally.

In the temporal dimension the currently existing systems may
feel quite well protected from the effects of the systems that
are to replace them in the future. It is the present
generation that affects the future ones. Therefore in this
dimension the condition becomes primarily a moral issue that
leads to studies of intergenerational equity and justice
(Costanza, Daly 1992, Golley, 1994, Glasser et al., 1994).
Spatially the systems have more obvious bi-directional
feedbacks and respond to mismanagement in quite remote
locations.

This condition is strongly related to educational and
traditional backgrounds that identify the value sets to be
applied. Some of the actions are much easier to exclude by a
taboo-type rules, rather than by common sense and logical
reasoning. In a way this relates the goals of sustainability
to some of the fields addressed by faith and religion. In
each particular case the issue of harm can be different. It
very much depends on the existing trade-offs between different
subsystems and their mutual willingness to cope with the
inconveniences created by different close and remote
neighbors. The only fact that a certain subsystem generates
toxic waste of a certain type does not make it totally
unbearable by the surrounding subsystems. There may be forms
of compensation that a polluting system can offer, either in
form of economic benefits or serving as sink for other types
of pollution in exchange. In any case this problem is
supposed to be resolved in a manner of mutual agreement and
fair play.

It is therefore important to identify the borders of the
system to be considered. For instance when speaking about
sustainable agriculture, we may look at a field or a farm as
the system to be taken care of. With adequate agricultural
practices and sufficient investments in the soil
rehabilitation procedures we may attain long-lasting
sufficiently high yields. However analyzing the
sustainability of such a system we are to take into account
the sources of, say, energy used, fertilizers and manure
applied, etc. In this way it may easily turn out that the
energy has been produced in a non-sustainable manner, or the
production of fertilizers was generating pollution, and so on.
It becomes a question then whether the particular agricultural
field in this case can be considered a sustainable system.
Similar examples may be found in larger and smaller scales.
After choosing the system borders the next step is to trace
all the inputs and outputs and analyze the pathways of
information and material coming into and leaving the system.
This first principle may be helpful in setting certain
restrictions within the systems, so that local borders can be
defined, otherwise we shall inevitably end up at the global
scale.

The second condition for sustainability is also quite obvious
if we want the system to be sustained. If the living
conditions in a certain region no longer suit the people
living there, it results in social tension that eventually
reorganizes the social and economic components of the system.
This occurs in form of gradual depopulation (emigration or die-
off), or sharp conflict (wars, revolutions), that changes both
the numbers and the system structure. In any case the system
is to change its initial design and therefore is to fail the
sustainability test. Important is the mode of change. In
sustainable systems the change takes place as a result of
actions accepted by the society and not causing conflict
(discomfort, discontent). The same events occurring against
the societal choice make the system unsustainable.

This can be also considered in the perceptual framework. The
living standards and living patterns are very much a function
of local traditions and education. The living standards that
would seem luxurious for a family with little wealth would
turn out to be insufficient for somebody who is already well-
off. These differences become further pronounced when
comparing across different cultures and traditions. The
living standards that seem acceptable and even desirable in
some countries would hardly suit people in other parts of the
world. In many cases the best solution for attaining
sustainability is to decrease material desires by shifting
priorities in people's value systems. We are therefore
inclined to be looking not at an absolute indicator of life
quality in terms of GNP or market price, but as we formulated
above at the content and comfort of the inhabitants.

A corollary that follows from this condition is that it is
hardly possible to achieve sustainability in the developing or
transient economies in such regions as Africa or Former Soviet
Union. Economic transitions assume wide shifts in social and
political institutions, they become possible as a result of
discontent and rejection of the status quo by the majority of
the population. This is a stage of reconstruction, which can
be hardly associated with sustainability.

The third condition parallels the second, but for the biotic,
ecological component of the system. It is therefore important
to identify the signals of the ecosystem that would
communicate its "content" or "comfort" for the given state.
This implies a set of some overall ecological indicators or
indices. The intensively developed concept of ecosystem
health (Costanza et al., 1992) may be useful at this stage.
In this way the ecosystem health notion is used to identify
system sustainability, rather than the sustainability concept
applied for identifying the ecosystem health.
The current conditions of the system are an important factor
in deciding whether the system should be sustained or not. On
the other hand the property of system sustainability depends
upon the current conditions of the system. For certain
conditions sustainability may not be achieved. This again
parallels sustainability with stability, when stable dynamics
was a function of the initial conditions of the system. In
case of sustainability there is more flexibility in achieving
the desired state due to the external controls at our disposal
-- theoretically we may always assume new technologies or
methods that would solve all the problems and bring the system
to the desired regime. However in practice there are always
limits (defined by the available resources or time).

The perceptual look at sustainability produces a different set
of indicators. While speaking about resource sustainability
the indicators that are usually suggested tend to be
measurable and continuous. The kind of axiomatic definition
given above results in indicators of a discrete type: yes or
no, either the system complies with the listed conditions or
not. In this case we do not want to compare systems with
respect to their sustainability, to define which system is
more sustainable, which is less. We do not assume
intermediate stages: either the system is sustainable and then
it satisfies all the restrictions, or it is not sustainable.
We may note that these conditions for sustainability merge the
ecological and economic into one system. The three conditions
meet the criteria of dealing with the temporal, spatial, and
structural dimensions common to sustainability definitions.
They may be applied only in the level of general system
dynamics. Therefore sustainability becomes a general systems
property, when all the variety of system components are taken
into account. To coin a term for such sustainable systems, we
may call them sustems, and try to promote sustems analysis.

Acknowledgments

The research has been supported by a grant from the Center for
Analysis of Environmental Change, Oregon State University. We
thank Richard Gale and Jim Wigington for stimulating
discussions.

References

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